4Fe + 3O2 → 2 Fe2O3

What do you notice about the atoms in this equation?

Word Equation:Acetic acid + sodium hydrogen carbonate --→ sodium acetate + water +carbon dioxide

Chemical Equation:H2C2H3O2 + NaHCO3 --→ NaC2H3O2 + H2O + CO2

Reactant Product“produces” or “yields”

Subscript: H2O – tells you how many of one particular atom

Coefficient: 2H2O – tells you how many molecules

Balancing Act

Atoms are not CREATED or DESTROYED during a chemical reaction.

• Scientists know that there must be the SAME number of atoms on each SIDE of the EQUATION.

• To balance the chemical equation, you must add COEFFICIENTS in front of the chemical formulas in the equation.

• You cannot ADD or CHANGE subscripts!

How to Balance Equations:

• Step 1: Determine number of atoms for each element.

• Step 2: Pick an element that is not equal on both sides of the equation.

• Step 3: Add a coefficient in front of the formula with that element and adjust your counts.

• Step 4: Continue adding coefficients to get the same number of atoms of each element on each side.

Mg + O2 → MgO

Step 1: Determine number of atoms for each element.

Mg = 1 Mg = 1O = 2 O = 1

Mg + O2 → MgO

Step 2: Pick an element that is not equal on both sides of the equation.

Mg = 1 Mg = 1O = 2 O = 1

Since the O atoms are not equal,we’ll target those first!

Mg + O2 → MgO

Step 3: Add a coefficient in front of the formula with that element and adjust your counts.

Mg = 1 Mg = 1 2O = 2 O = 1 2

2

Adding a 2 in front of MgO willchange the number of atoms on theproduct side of the equation.

Mg + O2 → MgO

Step 4: Continue adding coefficients to get the same number of atoms of each element on each side.Mg = 1 2 Mg = 1 2O = 2 O = 1 2

2 2

Now we need to increase thenumber of Mg atoms we have on thereactant side. Adding a 2 in front ofMg will give us 2 atoms of Mg andbalance the equation.

Your Turn:

Balance the following equations. Be sure to show your work!

1. ____ Ca + ____ O2 → ____ CaO

2. ____ N2 + ____ H2 → ____ NH3

3. ____ Cu2O + ____ C → ____Cu + ____ CO2

4. ____ H2O2 → ____ H2O ____ O2